On Tue, Aug 2, 2016 at 6:38 PM, Cedric St-Jean <[email protected]>
wrote:
> I can't speak to Julia's branch prediction, but if you rewrite it as
>
> function f{x}(::Val{x}) ...
> ...
> end
>
> f(Val{True})
>
Don't do this.
>
> then the compiler will create two versions of f, one with the if and one
> without. Then you can @time the results and see if it makes a
>
Which is generally bad except for synthetic benchmarks except for rare
cases.
> difference.
>
>
> On Tuesday, August 2, 2016 at 5:29:41 AM UTC-4, esproff wrote:
>>
>> So let's say I have a function of the form:
>>
>> function f(x::Bool)
>> for i in 1:10000000
>> *(bunch of stuff)*
>> if x
>> do something
>> end
>> *(even more stuff)*
>> end
>>
>
Julia doesn't do "branch prediction", that's the job of the CPU.
A branch with a constant branch condition basically has no cost anyway. You
are not (syntactically) evaluating anything millions of times.
>
>> As you can see I only need to evaluate this if statement once, but
>> instead I'm (in theory) evaluating it millions of times. How good is
>> Julia's branch prediction? Does Julia's JIT compiler recognize this and
>> make it so the if statement is only evaluated once?
>>
>
